What is the best way to add options to a select from a JavaScript object with jQuery?

The same as other answers, in a jQuery fashion:

$.each(selectValues, function(key, value) {        $('#mySelect')         .append($("<option></option>")                    .attr("value", key)                    .text(value)); });

var output = [];$.each(selectValues, function(key, value){  output.push('<option value="'+ key +'">'+ value +'</option>');});$('#mySelect').html(output.join(''));

In this way you "touch the DOM" only one time.

I'm not sure if the latest line can be converted into $('#mySelect').html(output.join('')) because I don't know jQuery internals (maybe it does some parsing in the html() method)

This is slightly faster and cleaner.

var selectValues = {  "1": "test 1",  "2": "test 2"};var $mySelect = $('#mySelect');//$.each(selectValues, function(key, value) {  var $option = $("<option/>", {    value: key,    text: value  });  $mySelect.append($option);});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script><select id="mySelect"></select>